1. Field of the Invention
The present invention relates to a so-called front-opening interface mechanical standard (FIMS) system used when wafers held in a transfer container which is called a pod are transferred among semiconductor processing apparatuses in a semiconductor manufacture process or the like. More specifically, the present invention relates to a purging apparatus and a purging method for cleaning the inner portion of a pod in the FIMS system in which the pod containing the wafers which is called a front-opening unified pod (FOUP) is placed and the wafers are moved from and into the pod.
2. Related Background Art
Up to now, a semiconductor manufacture process has been conducted in a so-called clean room in which a room in which semiconductor wafers are treated has high cleanliness. However, in order to deal with the increase of a wafer size and the reduction of a cost required to maintain the room clean, a method of maintaining the inner portion of a processing apparatus, the pod (wafer container), and a mini-environment for substrate transferred from the pod to the processing apparatus with a high cleanliness state is employed in recent years.
The pod includes a main body portion having a substantially cube shape and a lid. The main body portion includes a rack capable of holding a plurality of wafers therein in a state in which the wafers are separated from one another in parallel and an opening portion which is provided on a surface of the main body and is used for wafer transfer. The opening portion is closed with the lid. A pod in which a forming surface of the opening portion is located not vertically below the pod but on a side surface of the pod (in front of the mini-environment) is generically called a front-opening unified pod (FOUP). The present invention is mainly for arrangemants using the FOUP.
The above-mentioned mini-environment includes a first opening portion opposed to the opening portion of the pod, a door for closing the first opening portion, a second opening portion provided on a semiconductor processing apparatus side, and a transfer robot that moves from the first opening portion to the inner portion of the pod to hold the wafer and passes through the second opening portion to transfer the wafer to the semiconductor processing apparatus side. A structure for forming the mini-environment includes a mount base for supporting the pod so that the opening portion of the pod is simultaneously opposed to the front surface of the door.
A positioning pin inserted into a positioning hole provided on a lower surface of the pod to regulate a mount position of the pod and a clamp unit engaged with a portion to be clamped which is provided on the lower surface of the pod to hold the pod to the mount base are located on an upper surface of the mount base. The mount base is normally movable back and forth with respect to a direction toward a door by a predetermined distance. When the wafers in the pod are to be transferred to the processing apparatus, the pot is moved in a state in which the pod is mounted until the lid of the pod comes in contact with the door. After that contact, the lid is removed from a position at which the lid closes the opening to open the pod. Therefore, the inner portion of the pod is connected to the inner portion of the processing apparatus through the mini-environment. Subsequently, wafer transfer operation is repeated. A system including the mount base, the door, the first opening portion, a door opening/closing mechanism, and a wall which is a part of the mini-environment including the first opening portion is generally called a front-opening interface mechanical standard (FIMS) system.
An inner portion of the pod storing the wafers and the like is normally filled with dry nitrogen or the like which is maintained to a highly clean state, thereby preventing contaminants, an oxidizing gas, or the like from entering the inner portion of the pod. However, the pod stores wafers passing through a processing chamber, so there may be the case where contaminants or the like are deposited on the wafers in the processing chamber or the like and the wafers on which the contaminants are deposited are taken in the pod. When the wafers on which the contaminants or the like are deposited are taken in a subsequent processing chamber, desirable wafer processing which is normally performed by passing through the subsequent processing chamber is impossible in some cases. Therefore, when the wafers are transferred from the pod to a transfer chamber, it is necessary to remove the contaminants or the like.
In the conventional FOUP, in order to meet such a requirement, a gas supply port for introducing a purge gas into the pod and an gas evacuation port for evacuating the purge gas from the pod are provided in a bottom portion of the pod. The gas supply port and the gas evacuation port are connected to a purge gas supply port and a purge gas evacuation port, respectively, which are provided in a support base on which the pod is placed. According to actual operation, a high-pressure gas which is maintained to a highly clean state is introduced from the support base side into the pod through the gas supply ports. Simultaneously, gases and contaminants which are present in the inner portion of the pod are evacuated to the outside of the pod through the gas evacuation ports. The contaminants or the like deposited on the wafer taken in the pod are removed by the above-mentioned operation.
However, when the high-pressure gas is merely introduced from the bottom portion of the pod, the gas may flow through mainly the vicinities of the circumferences of wafers through which the gas easily passes. Therefore, it may be difficult to pass a gas having a sufficient flow rate through spaces above and below each of the wafers held at minute intervals. The contaminants or the like are deposited mainly on an upper surface of each of the wafers or a lower surface thereof, so it may be difficult to sufficiently remove the contaminants or the like by a conventional method. Such a situation may become more significant with an increase in wafer size. Therefore, more suitable removal methods are desired.
A method disclosed in JP 2003-045933 A is proposed as a method of surely removing the contaminants deposited on the wafer. According to this method, a space for storing an opener, which is separated from the transfer chamber, is provided. The space includes a gas supply port located above the front surface of an opening portion of the pod. A clean gas is supplied to the inner portion of the pod through the gas supply port and circulated through the inner portion of the pod. The clean gas flowing from a lower portion of the pod to the space is evacuated from a lower portion of the space. When the clean gas is circulated through the inner portion of the pod using such a structure, the contaminants or the like can be more surely removed as compared with the conventional method.
A method of introducing a clean gas between adjacent wafers held in the inner portion of the pod is disclosed in JP 11-251422 A. According to this method, a gas introducing flow path and a gas evacuating flow path which are communicated with each of groove portions for storing each of the wafers are provided in the inner portion of the pod. A clean gas is blown to the surface of each of the wafers through the gas introducing flow path and a clean gas containing the contaminants or the like is evacuated through the gas evacuating flow path, so that the contaminants can be more surely removed.
According to the method disclosed in JP 2003-045933 A, some degree of effect can be expected with respect to reductions in humidity of the inner portion of the pod and in the amount of oxidizing gas thereof, and prevention of organic contamination. However, it may be also difficult to perform effective replacement on gases or the like which are present between adjacent wafers held with a minute space. Therefore, it may be similarly difficult to obtain an effect in which the contaminants deposited on the upper and lower surfaces of each of the wafers are removed.
According to the method disclosed in JP 11-251422 A, the contaminants deposited on the upper and lower surfaces of the wafer can be removed. However, it may be difficult to provide a gas introducing flow path having a large inner diameter in view of an actual structure. Therefore, it is expected that a pressure difference of a gas introduced to the surface of the wafer or a difference of time for which the gas is introduced at a predetermined pressure is caused between the upstream of this flow path and the downstream thereof, and thus a contaminant removal effect varies according to a position in which the wafer is held.
The support base, a shape of the pod, arrangements of the clean gas supply port and the gas evacuation port which are provided for purging of the inner portion of the pod, and the like are substantially standardized in the semiconductor manufacture industry. Therefore, there is a problem in that the system disclosed in JP 2003-045933 A or the pod disclosed in JP 11-251422 A, which requires a structure different from that of this standard cannot be commonly applied to the support base and the like which are currently normally used.